As is well known in the art, glassy metal alloys are rapidly quenched or cooled at a rate on the order of 10.sup.6 .degree. C. per second from a liquid state to a substantially amorphous solid state. The cast ribbon is typically formed by extruding molten alloy from a pressurized reservoir through a restricted orifice of a nozzle onto a high-speed cooling surface. The cast ribbons are necessarily thin (i.e. up to only approximately 2 mils thick) due to the extreme heat transfer requirements for preventing substantial crystallization.
Glassy or amorphous metal alloys produced in this manner are of considerable technological interest. Specifically, such alloys exhibit unique electrical and magnetic properties that allow the production of, for example, electrical transformers and motors of markedly improved efficiency.
Wound cores and flat laminations can be produced from the ribbons in a nearly unlimited variety of dimensions (width/thickness) as required to meet specific applications. While ribbons of virtually any controlled width may be cast, market volume for a particular width of ribbon may not be sufficient to cover costs for setting up for direct production each time.
Further, ribbons cast to a particular width dimension can suffer from edge burrs, voids and pockets due to molten metal interaction with boundary layer air and/or dirt and contaminants on the surface of the chill substrate adjacent the lateral edges, as well as on the walls of the casting nozzle or on nozzle dividing elements. Disadvantageously, uneven, burred edges can reduce ribbon packing densities and thereby adversely affect the performance of the electrical machinery having components made from the ribbon. Thus, it is clear that a need exists for a method of cleanly slitting and/or trimming- wide ribbons or sheets of amorphous material into strips of desired width for further processing into electrical components and the like.
A number of ribbon cutting or slitting processes have been provided in the past. These include die punching and laser cutting operations. While each of these processes is capable of slitting the cast amorphous ribbon, they are not without their disadvantages.
Since metallic glass alloys have a high hardness (greater than Rockwell 62) and require high stresses to initiate plastic deformation, the punching operation is difficult. Further, the dies in the punching process wear rapidly resulting in approximately 1/100 to 1/1000 the normal service life. In addition, some economical metals, such as Fe-B, Fe-B-Si-C amorphous alloys, are brittle in thicknesses greater than 1 mils and therefore are subject to crack formation and breaking during punching. When the punched strips of amorphous metal are annealed at the Curie point to enhance magnetic properties, they are also subject to a loss of ductility. As a result, any cracks left from the punching process can act as stress risers when the laminations are put together. This, of course, leads to shattering from edge cracks and premature failure.
Laser cutting processes do avoid many of the problems noted above with respect to punching operations but, unfortunately, they also suffer from their own inherent drawbacks. In laser cutting a high energy beam creates a high temperature spot on the amorphous metal material that melts and separates the material into strips of the desired width. As the amorphous material is heated, however, a greater portion of the laser beam is reflected. As a result, it is difficult to maintain controlled power delivery to the cutting region. Consequently, through overcompensation and an increase in power, the amorphous structure may be lost adjacent the cut edge through the recrystallization of the strip material. In addition, cutting speeds using lasers are relatively slow and therefore not cost efficient for processing.
With a background of these difficulties, others skilled in the art have been lead in another direction to still another technique; that is, slitting by producing a controlled disturbance in the molten puddle of the cast ribbon. This technique is described and claimed in U.S. Pat. No. 4,527,613, issued July 9, 1985 and assigned to Electric Power Research Institute. While this process is generally successful for its intended purpose, it is of course limited to having to be carried out during the initial casting process before solidification into an amorphous ribbon. In several respects this procedure is less desirable. For example, it is more economical to cast and stock the ribbon in a universal width and then cut or trim to the width needed, when needed.
A need is, therefore, identified for a new and improved method and apparatus for cutting or slitting solidified amorphous metal ribbon while maintaining the desirable electrical, mechanical and magnetic properties of the material.